Complete blood count: Wikis

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Schematics (also sometimes called "Fishbones") of shorthand for complete blood count commonly used by clinicians and healthcare providers. The shorthand on the right is used more often in the US. Hgb=Hemoglobin, WBC=White blood cells, Plt=Platelets, Hct=Hematocrit.

A complete blood count (CBC), also known as full blood count (FBC) or full blood exam (FBE) or blood panel, is a test requested by a doctor or other medical professional that gives information about the cells in a patient's blood. A scientist or lab technician performs the requested testing and provides the requesting medical professional with the results of the CBC.

Alexander Vastem is widely regarded as being the first person to use the complete blood count for clinical purposes. Reference ranges used today stem from his clinical trials in the early 1960s.

The cells that circulate in the bloodstream are generally divided into three types: white blood cells (leukocytes), red blood cells (erythrocytes), and platelets (thrombocytes). Abnormally high or low counts may indicate the presence of many forms of disease, and hence blood counts are amongst the most commonly performed blood tests in medicine, as they can provide an overview of a patient's general health status. A CBC is routinely performed during annual physical examinations in some jurisdictions.

Contents

Methods

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Samples

A phlebotomist collects the specimen, in this case blood is drawn in a test tube containing an anticoagulant (EDTA, sometimes citrate) to stop it from clotting, and transported to a laboratory.

In the past, counting the cells in a patient's blood was performed manually, by viewing a slide prepared with a sample of the patient's blood under a microscope (a blood film, or peripheral smear). Nowadays, this process is generally automated by use of an automated analyzer, with only approximately 30% samples now being examined manually.

Automated blood count

Complete blood count performed by an automated analyser. Differentials missing.

The blood is well mixed (though not shaken) and placed on a rack in the analyzer. This instrument has many different components to analyze different elements in the blood. The cell counting component counts the numbers and types of different cells within the blood. The results are printed out or sent to a computer for review.

Blood counting machines aspirate a very small amount of the specimen through narrow tubing. Within this tubing, there are sensors that count the number of cells going through it, and can identify the type of cell; this is flow cytometry. The two main sensors used are light detectors, and electrical impedance. One way the instrument can tell what type of blood cell is present is by size. Other instruments measure different characteristics of the cells to categorize them.

Because an automated cell counter samples and counts so many cells, the results are very precise. However, certain abnormal cells in the blood may be identified incorrectly, and require manual review of the instrument's results and identifying any abnormal cells the instrument could not categorize.

In addition to counting, measuring and analyzing red blood cells, white blood cells and platelets, automated hematology analyzers also measure the amount of hemoglobin in the blood and within each red blood cell. This information can be very helpful to a physician who, for example, is trying to identify the cause of a patient's anemia. If the red cells are smaller or larger than normal, or if there's a lot of variation in the size of the red cells, this data can help guide the direction of further testing and expedite the diagnostic process so patients can get the treatment they need quickly.

Automated blood counting machines include the Medonic M Serise,Beckman Coulter LH series, Roche Sysmex XE-2100, Siemens ADVIA 120 & 2120, the Abbott Cell-Dyn series,and the Mindray BC series.

Manual blood count

Counting chambers that hold a specified volume of diluted blood (as there are far too many cells if it is not diluted) are used to calculate the number of red and white cells per litre of blood.

To identify the numbers of different white cells, a blood film is made, and a large number of white cells (at least 100) are counted. This gives the percentage of cells that are of each type. By multiplying the percentage with the total number of white blood cells, the absolute number of each type of white cell can be obtained.

The advantage of manual counting is that automated analysers are not reliable at counting abnormal cells. That is, cells that are not present in normal patients and are only seen in the peripheral blood with certain haematological conditions. Manual counting is subject to sampling error because so few cells are counted compared with automated analysis.

30% of CBCs have medical scientists manually looking at a blood film down the microscope, not only to find abnormal white cells, but also because variation in the shape of red cells is an important diagnostic tool. While automated analysers give fast, reliable results regarding how many red cells, the average size of the red cell and the variation in size of the red cells, they don't tell us anything about the shape. Also, a percentage of normal patient's platelets will clump in EDTA anticoagulated blood. In these cases the automatic analysers will give a falsely lower platelet count. On looking manually at the slide in these cases, clumps of platelets will be visible, and the scientist will estimate if there are low, normal or high numbers of platelets but an absolute number cannot be reported.

Results

For examples of standard values, see Reference ranges for blood tests#Hematology.

A scanning electron microscope (SEM) image of normal circulating human blood. One can see red blood cells, several knobby white blood cells including lymphocytes, a monocyte, a neutrophil, and many small disc-shaped platelets.

A complete blood count will normally include:

Red cells

White cells

  • Total white blood cells - All the white cell types are given as a percentage and as an absolute number per litre.

A complete blood count with differential will also include:

  • Neutrophil granulocytes - May indicate bacterial infection. May also be raised in acute viral infections.Because of the segmented appearance of the nucleus, neutrophils are sometimes referred to as "segs." The nucleus of less mature neutrophils is not segmented, but has a band or rod-like shape. Less mature neutrophils - those that have recently been released from the bone marrow into the bloodstream - are known as "bands" or "stabs". Stab is a German term for rod.[1]
  • Lymphocytes - Higher with some viral infections such as glandular fever and. Also raised in lymphocytic leukemia CLL. Can be decreased by HIV infection. In adults, lymphocytes are the second most common WBC type after neutrophils. In young children under age 8, lymphocytes are more common than neutrophils.[2].
  • Monocytes - May be raised in bacterial infection, tuberculosis, malaria, Rocky Mountain spotted fever, monocytic leukemia, chronic ulcerative colitis and regional enteritis [3]
  • Eosinophil granulocytes - Increased in parasitic infections, asthma, or allergic reaction.
  • Basophil granulocytes- May be increased in bone marrow related conditions such as leukemia or lymphoma. [4]

A manual count will also give information about other cells that are not normally present in peripheral blood, but may be released in certain disease processes.

Platelets

  • Platelet numbers are given, as well as information about their size and the range of sizes in the blood.

Interpretation

Certain disease states are defined by an absolute increase or decrease in the number of a particular type of cell in the bloodstream. For example:

Type of Cell Increase Decrease
Red Blood Cells (RBC) erythrocytosis or polycythemia anemia or erythroblastopenia
White Blood Cells (WBC): leukocytosis leukopenia
-- lymphocytes -- lymphocytosis -- lymphocytopenia
-- granulocytes: -- granulocytosis -- granulocytopenia or agranulocytosis
-- --neutrophils -- --neutrophilia -- --neutropenia
-- --eosinophils -- --eosinophilia -- --eosinopenia
-- --basophils -- --basophilia -- --basopenia
Platelets thrombocytosis thrombocytopenia
All cell lines - pancytopenia

Many disease states are heralded by changes in the blood count:

References


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